Spirochetes are a group of medically important bacteria which have been poorly studied. We do not understand some of the most fundamental aspects of nutrition, structure and function, and mechanisms of pathologenesis. One unique aspect of all spirochetes is rapid motility and distinct structure. As compared to other flagellated bacteria, where the flagella are external to the cell wall, spirochetes contain flagella-like structure (axial filaments) which are internal. That is, these filaments and the bacteria are ensheathed by a membrane. It is difficult to understand at this time how they propel themselves. We do not even know if these axial filaments play a role in motility. We propose to use a genetic-structural and biochemical approach towards understanding how spirochetes move. We are using Leptospira as our model system, as these spirochetes are the easiest to grow in the laboratory. Our future plans include similar experiments on oral treponemes once the methodology has been developed. Our approach is to mutagenize Leptospira with nitrosoguanidine and ultraviolet light and isolate colonies which do not spread on agar. Presumably these bacteria will be motility mutants, as determined by darkfield microscopy. We have isolated a number of such mutants by this technique. Our next step is to analyze these mutants by electron microscopy and by chemical analysis of the mutant axial filaments. We have found that many of these motility mutants synthesize aberrant axial filaments as observed by electron microscopy. This is the first suggestive evidence that axial filaments play a role in spirochete motility. We are now purifying these filaments and comparing them morphologically and chemically to normal filaments. Our final step is to analyze whether motility revertants of these mutants regain normal axial filaments. The results would indicate whether the combined motility and aberrant axial filament phenotypes are the result of a pleotrophic mutant or multiple mutations.